Re: Quick-and-dirty compression for WAL backup blocks

Heikki Linnakangas <hlinnaka@iki.fi> writes:
> Vacuum doesn't zero out the free space between lower and upper,

It does now ;-)

> How about adding a flag to XLogRecData to indicate if the space between 
> pd_lower and pd_upper is meaningful or not? The XLogInsert caller probably 
> knows that. That way you could completely skip over the free space if 
> it's not meaningful, saving even more cycles.

Hmm ... that might not be a bad idea.  As far as I can think offhand,
all the XLogInsert callers know very well what type of page they are
working with, so they would always be able to set such a flag correctly.

Would this be institutionalizing a particular approach to data
compression in the XLogInsert API, though?
        regards, tom lane